1. Field of the Invention
The present invention relates to a refrigerant pump for use in a cooling apparatus for cooling a highly exothermic semiconductor element or the like by utilization of a change in phase of a refrigerant between evaporation and condensation thereof.
2. Description of the Related Art
An exemplary refrigerant pump such as disclosed in, for example, Japanese Patent Publication No. 7-47957, first published Nov. 21, 1990 under Publication No. 2-283887, is reproduced in FIGS. 5 and 6 of the accompanying drawings, which illustrate a longitudinal sectional view of the prior art refrigerant pump and a cross-sectional view taken along line A—A in FIG. 5, respectively. As shown in FIGS. 5 and 6, the prior art refrigerant pump utilizes a thick-walled intermediate shell 52 for supporting a pump mechanism 53 that is enclosed within a thin-walled hermetic vessel 51. A rotor of an electric motor unit employed in this prior art refrigerant pump has a plurality of parallel holes 54 defined therein for the flow of a refrigerant therethrough. A suction plate 55 has a suction port 61 defined therein so as to open radially outwardly and is fixedly positioned with the suction port 61 oriented upwardly. A suction tube 56 and a discharge tube 57 are disposed in alignment with the longitudinal axis of the refrigerant pump. In this structure, a pump-side bearing 58 and a cylinder 59 accommodating the pump are separated from each other while a drive shaft 50 is rotatably supported by the suction plate 55.
In the prior art refrigerant pump of the structure discussed above, the intermediate shell is used to alleviate strains that may be developed during welding. However, the use of this intermediate shell is an addition to the number of the component parts, making it difficult to center the drive shaft and the bearing with each other in the face of accumulation of allowances of the component parts. Accordingly, the prior art refrigerant pump under discussion has a problem in that when the drive shaft and the bearing are mounted in a fashion offset relative to each other, the rotational torque tends to increase to such an extent as to result in failure to rotate smoothly. Also, since the assembly is enclosed within the thin-walled hermitic vessel, it requires the drawing process to be performed with utmost care to secure a dimensional accuracy and this is indeed difficult to achieve.
In addition, since the rotor of the electric motor unit is perforated to define the refrigerant passages, an additional problem has arisen in that at a high speed operation the refrigerant will not satisfactorily flow into the refrigerant passages, resulting in a reduction of the amount of the refrigerant being circulated. Yet, since the rotor employed is a direct current motor having magnets inserted therein, it is indeed difficult to secure a space for definition of the refrigerant passages particularly where the rotor has a small diameter. Considering that in the prior art refrigerant pump the suction port in the suction plate has a final suction end defined on the top of the suction plate, there is a good chance that a gas of the refrigerant may enter the refrigerant pump and, once this happens, the amount of the refrigerant being circulated would decrease to such an extent as to result in abrupt drop of the cooling performance. This abrupt drop of the cooling performance does in turn bring about damages to a highly exothermic semiconductor element. In addition, since the suction tube is disposed in alignment with the longitudinal axis of the refrigerant pump, it often occurs that the refrigerant pump may be operated with the gas admixed therein. On the other hand, since the discharge tube is also disposed in alignment with the longitudinal axis of the refrigerant pump, the refrigerant cannot be positively accumulated within the refrigerant pump.
In recent years, demands have arisen to reduce the height of the refrigerant pump particularly where the refrigerant pump is to be incorporated into a rack-type frame structure of a limited height.
Also, since the pump-side bearing and the cylinder are separated from each other, it has been necessary to assemble the refrigerant pump while a careful centering work is performed. Moreover, since the hole in the cylinder is offset from the longitudinal axis of the cylinder, it has been necessary to assemble the refrigerant pump without misalignment.